Report: U.S. averages nearly one mass shooting per day so far in 2017

As thousands of concertgoers in Las Vegas fled a barrage of bullets fired from hundreds of feet away, and 32 floors up, Sunday night, the hundreds who were hurt or killed became the victims of the 273rd mass shooting in the U.S. this year.

Sunday was the 274th day of the year.

Those shootings have left more than 1,500 people injured, and more than 300 dead, according to the non-profit Gun Violence Archive, which tracks and catalogs incidents in which at least four people, not counting the shooter, are injured or killed in a shooting. These numbers include the Las Vegas attack, for which the total number of dead and injured is still being assessed.

The incidents, as they do every year, spanned the country, occurring in cities, rural communities and suburbs in nearly every state.

"This doesn't stop, I have not had a vacation since 2013," said Mark Bryant, who runs the Gun Violence Archive along with about 20 paid researchers and staffers, most of whom he says have master's or higher-level degrees in library science and other research fields.

Paddock, 64, began shooting from the window of his room on the 32nd floor of the Mandalay Bay Resort and Casino just after 10 p.m. local time Sunday evening, police said. A SWAT team found Paddock dead in his hotel room and suspect he killed himself. Police said Monday morning that Paddock had "at least 10 rifles" in the room; they later reported finding a total of 23 firearms.

In addition to being the 273rd mass shooting this year, the Las Vegas attack was the 18th mass murder — incidents in which at least four people, other than the shooter, were killed — cataloged by the Gun Violence Archive this year. The other deadly attacks left 83 dead and 13 wounded.

This is the deadliest 72-hour span of gun violence so far this year. Second deadliest span was 123 gun deaths on June 19th. https://t.co/ysEWtfl5KW

In a phone call with CBS News Tuesday, Bryant noted that on Oct. 2 last year, there had already been 292 mass shootings in the U.S., but that the attack in Vegas will push the injury totals for this year far past those of last year.

Bryant said the organization began keeping track of gun violence in 2013, seeking to produce more accurate reporting than was publicly available.

On a near hourly basis, the Archive updates with new information about gun-related incidents, typically with up to 140 data points, often even street-level information about the shootings.

The Gun Violence Archive does not track motives for attacks, but does track unintentional, defensive, and home invasion-related attacks, as well as ones in which children or teens are injured or killed, and incidents in which deaths or injuries to police or the shooters themselves occur. The organization does keep data on the types of guns used in mass shootings, but that information was not immediately available.